Treatment of slaugtherhouse wastewater by upflow anaerobic sludge blanket microfiltration osmotic membrane bioreactor

In this study, it was aimed to investigate the performance of the upflow anaerobic sludge blanket microfiltration osmotic membrane bioreactor (UASB MF-OMBR) system in the treatment of slaughterhouse wastewater and to compare the results of treatment performance, flux variation, microbial community shift, and membrane fouling with an anaerobic microfiltration osmotic membrane bioreactor (AnMF-OMBR). In the first stage of the study, the effects of increasing draw solution (DS) concentration on system performance were determined by operating the systems at different DS concentrations (0,47 M, 1 M, and 1,5 M) and the critical DS concentration was determined. In the systems operated at different DS concentrations, treatment performance decreased with increasing DS concentration, resulting in chemical oxygen demand (COD) removal efficiency of 41–23% in the AnMF-OMBR and 43–26% in the UASB MF-OMBR for 0,47 M, 1 M, and 1,5 M DS concentrations. In the systems operated at 0,47 M, 1 M, and 1,5 M DS concentration, the methane production decreased with increasing DS concentration and was in the range of 0,19–0,14 L CH4/g CODremoved in the AnMF-OMBR and 0,24–0,19 L CH4/g CODremoved in the UASB MF-OMBR. It was determined that COD rejection was not affected by the increasing DS concentration in both bioreactors and high COD rejections (>93%) were obtained throughout the entire operating period. While NH4+-N rejections decreased with increasing DS concentration (87–79% in the AnMF-OMBR; 91–81% in the UASB MF-OMBR), PO43--P rejections did not show a significant change (for both systems >91%). As a result of Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy-energy diffusive X-ray (SEM-EDX), and confocal laser scanning microscopy (CLSM) analyses performed on the fouled forward osmosis (FO) membranes operated at different DS concentrations, it was determined that the membrane fouling became more severe with increasing DS concentration. The effect of DS concentration on flux values was examined in the systems operated at different DS concentrations. Initial flux values (Jw) in the systems operated at 0,47 M, 1 M, and 1,5 M DS were 8,7 L/m².h, 9,0 L/m².h and 10,6 L/m²h in the AnMF-OMBR, respectively, and 10,63 L/m².h, 11,20 L/m².h and 11,74 L/m².h in the UASB MF-OMBR, respectively. It was observed that with the increasing DS concentration, JW values in the systems increased, but the flux decrease was greater during the operation. According to the results of the analytical hierarchy process (AHP) analysis based on FO performance, anaerobic performance, water recovery, microbial inhibition, and operation time parameters, 0,47 M DS concentration was determined as the critical DS concentration. Additionally, it was found that the microbial community in the systems was affected by salinity build-up, high free ammonia, and low organic loading rate (OLR). In the second stage of the study, the effect of COD concentration increase (5000 mg/L and 7500 mg/L) on the performance of the AnMF-OMBR and UASB MF-OMBR systems operated at 0.47 M DS concentration was investigated. It was determined that by increasing the COD concentration from 5000 mg/L to 7500 mg/L, the total Kjeldahl nitrogen (TKN) concentration in the wastewater increased from 780 mg/L to 1300 mg/L. It was observed that the treatment performance deteriorated (54–67%), especially in the AnMF-OMBR, by increasing NH4+-N due to the increasing COD concentration of wastewater. In the UASB MF-OMBR, it was determined that anaerobic activity was less affected (70%) by the increase in the COD. The COD rejection was not affected by the increase in the COD concentration and was >92% in both systems. Methane production also decreased as a result of the increasing NH4+-N concentration. It was determined as 0,16 L CH4/g CODremoved in the AnMF-OMBR and 0,18 L CH4/g CODremoved in the UASB MF-OMBR at the end of the study. With increasing COD concentrations, supernatant NH4+-N concentrations also increased, and this caused inhibition of anaerobic activity in the bioreactors. NH4+-N rejections were achieved as 66% and 64% in the AnMF-OMBR and 69% and 72% in the UASB MF-OMBR, respectively, at 5000 mg/L and 7500 mg/L COD concentrations. Similar high PO43--P rejections (>89%) were obtained in both systems. Initial flux values were determined as 9,61–5,99 L/m².h in the AnMF-OMBR and 9,96–6,79 L/m².h in the UASB MF-OMBR in operation with COD concentrations of 5000 mg/L and 7500 mg/L. As a result of autopsy analyses (FTIR, AFM, SEM-EDX) performed on the fouled FO membranes, it was determined that membrane fouling was less in the UASB MF-OMBR, where better treatment performance and flux were obtained than in the AnMF-OMBR. As a result of NGS analysis, it has been determined that the microbial community was affected by increasing COD concentrations and operating conditions (low OLR and high NH4+-N concentration), and the methane production was produced through acetate rather than hydrogen and carbon dioxide. Additionally, struvite and MgPO4- precipitation occurred in the systems operated at both different DS and COD concentrations. As a result, in this study, it was determined that slaughterhouse industry wastewater can be effectively treated with the innovative UASB MF-OMBR system. Compared to the AnMF-OMBR system, it was determined that the UASB MF-OMBR system showed better performance due to its configuration, especially in terms of flux performance and membrane fouling, and was less sensitive to salt and ammonia inhibitions.